1. Field of the Invention
This invention relates to improved hydrocarbon fuels and engine lubricants which reduce the octane requirements of gasoline-powered automotive engines.
The octane requirement increase (ORI) effect exhibited by internal combustion engines, e.g. spark ignition engines, is well known in the art. This effect may be described as the tendency for an initially new or clean engine to require higher octane quality fuel as operating time accumulates, and is coincidental with the formation of deposits in the region of the combustion chamber of the engine. Thus, during the initial operation of a new or clean engine, a gradual increase in octane requirement (OR), i.e. fuel octane number required for knock-free operation, is observed with an increasing build up of combustion chamber deposits until a rather stable or equilibrium OR level is reached which, in turn, seems to correspond to a point in time where the quantity of deposit accumulation on the combustion chamber and valve surfaces no longer increases but remains relatively constant. This so-called "equilibrium value" is usually reached between about 3,000 and 20,000 miles or corresponding hours of operation. The actual equilibrium value of this increase can vary with engine design and even with individual engines of the same design: however, in almost all cases the increase appears to be significant, with ORI values ranging from about 2 to 10 research octane numbers (RON) being commonly observed in modern engines.
It is also known that additives may prevent or reduce deposit formation, or remove or modify formed deposits, in the combustion chamber and adjacent surfaces and hence decrease OR. Such additives are generally known as octane requirement reduction (ORR) agents.
Development of an additive to control or reduce octane requirements of gasoline-powered automotive engines is particularly attractive now that car manufacturers are increasing compression ratios and optimizing ignition timing to meet increasingly stringent Federal fuel economy standards. Because of these more severe engine conditions, customer knock complaints have increased. Further, current trends indicate that most future model cars will not be satisfied by unleaded gasoline of 91 Research Octane Number, the minimum required by Federal Law. Since the demand for unleaded gasoline is increasing rapidly, it is becoming more difficult for oil companies to supply enough high octane unleaded gasoline. For these reasons, customer and car satisfaction could be increased by using gasoline additives that reduce or minimize the octane requirement increase resulting from engine deposits.
Accordingly, it is an object of this invention to provide a class of additive compositions suitable for use as ORR agents when combined with fuel and lubricants designed for use in spark-ignition internal combustion engines.
2. Description of the Prior Art
A number of patents have issued relating to use of urea derivatives to make improvements in gasoline compositions. U.S. Pat. No. 2,373,372 relates the use of alkylated and arylated ureas as antiknock improvers. U.S. Pat. Nos. 3,615,294 and 3,762,889 disclose detergent motor fuel compositions containing substituted ureas as the salt reaction product of a paraffinic oil oxidate and a substituted urea. U.S. Pat. No. 2,195,167 relates to a method of preventing the formation of gumlike products in lubricating oils by adding alkyl or aryl derivatives of urea to the oil. U.S. Pat. No. 2,657,984 discloses that the pour point of fuel oils can be improved by adding substituted ureas to the fuel oil.